1. Field of the Invention
The present invention relates to circuit boards generally and, more particularly, but not by way of limitation, to novel through hole circuit board interconnect and method that provide a via having high current carrying capability and improved manufacturing technique.
2. Background Art
Circuit boards are widely used in a variety of electrical/electronic applications and typically include a relatively thin planar substrate of a dielectric material having at least on the bottom side thereof conductive traces and pads. Such conductive traces and pads may also be formed on the upper surface of the substrate. Means are provided for mounting electrical/electronic components to the upper surface of the substrate. Such means include having mounting pins extending through the substrate or by the use of solder paste which is subsequently melted. Electrical/electronic components may also similarly be mounted to the lower surface of the substrate.
To conductively connect the opposite sides of the circuit board, vias are provided at selected locations when the board is manufactured. The vias are subsequently filled with a conductive material to effect electrical connections between the upper and lower surfaces. Then, the board is wave soldered in a conventional apparatus to electrically connect various elements on the lower surface of the board.
In an early technique, a conductive cylinder of a metallic material was formed around the walls of the vias using electroplating processes. Such technique, while providing relatively satisfactory connections, was expensive. In a further development, a conductive silver-epoxy material may be used to fill the vias. This technique is much less expensive than electroplating, but the silver-epoxy materials is limited in current carrying capacity to a continuous rating of about 300 mA maximum, whereas, in some applications, it would be desirable to provide much higher current ratings. Multiple parallel vias can be employed; however, limitations exist due to the amount of substrate space consumed to connect multiple vias in parallel, and the inability to guarantee even current sharing between the parallel connected vias because of via-to-via impedance variation.
In yet another development, solid pins are inserted into the vias to provide conductive connections. While not having the limited current rating of silver-epoxy filled vias, the pins require a separate process step, are not easily grasped, and cannot be used in the surface mounting tape for pick and place machines.
A further disadvantage of conventional circuit board manufacturing processes is that during the wave soldering step, gasses generated by the solder flux during heating can cause blowholes to be created in the wave soldered joints.
Accordingly, it is a principal object of the present invention to provide a through hole circuit board interconnect that has a relatively high continuous current rating.
It is a further object of the invention to provide a method of manufacture of such a through hole circuit board interconnect that avoids formation of blowholes during the wave soldering step.
It is an additional object of the invention to provide such through hole circuit board interconnect and method of manufacture that can easily be used in surface mount placement machines.
It is another object of the invention to provide such through hole circuit board interconnect and method of manufacture that are economical.
It is yet a further object of the invention to provide such through hole circuit board interconnect and method of manufacture that employ existing printed circuit board assembly processes and equipment.
It is yet an additional object of the invention to provide such through hole circuit board interconnect that consumes a minimum amount of space, preferably close to the size of a via.
It is yet another object of the invention to provide such a method of manufacture that inherently creates a vent path for gases formed during wave soldering.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.